block: blkdev_issue_secure_erase loop style

Use consistent coding style in this file. All the other loops for the
same purpose use "while (nr_sects)", so they win.

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20240223155910.3622666-2-kbusch@meta.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>